1. Field of the Invention
The present invention relates to a method for producing positive electrode materials of Li-ion secondary batteries, which are particularly suitable for being applied to mobile phones, portable computers, portable music players, etc.
2. Related Prior Art
The first commercialized lithium battery was developed by Japanese Sony Co. in 1990, in which a compound enabling Li ion to move in and out was used to form the negative electrode and replaced traditional lithium metal. Such secondary battery was rechargeable and safe in use. For the secondary battery, the positive electrode is usually made from a strong oxidant, for example, LiCoO2, LiNiO2 and LiMn2O4, the negative electrode is carbon, and the electrolyte is a non-aqueous solvent. Currently, the LiCoO2 battery is the major power supply for portable electronic devices because of higher charge capacity thereof. The LiNiO2 battery is disadvantageous in synthesis difficulties and poor heat stability. Compared with these two batteries, the LiMn2O4 battery is considered the best choice in cost, safety and environmental acceptance.
Traditionally, the solid-state reaction is used to produce the secondary batteries. However, the precursor powders have to be heated and grinded for a long time after mechanically blended, which may easily destroy their structure and thus reduces charge capacity.
In order to solve this problem, wet processes with advantages of easy blending, low-temperature synthesis and large specific surface area for reaction are applied to synthesize LiMn2O4 powders. The developed wet processes include sol-gel method, Pechini method and citric acid-gel method. Unfortunately, some drawbacks are still found in these wet processes, wherein the sol-gel method has to be carried out in an inert gas; the Pechini process is too expensive for mass production; and the drying procedure in the citric acid-gel method demands additional energy and cost.
Therefore, it is desirable to provide an improved method to mitigate and/or obviate the aforementioned problems.